With volatility returning to the market, it's become apparent that Wall Street pros have grown fearful. But what exactly do they fear?

Jim Cramer has an ear to the ground. Here are the concerns that he's hearing about:

Worry #1—Japan: "Frankly, it is downright scary what's happening in Japan," Cramer said. "This country's pretty much left the grid with what now looks like a failed strategy to get some sort of boom going. The Japanese stock market's down 14 percent this year, by far the worst major market in the world, and the country's retail sales have plummeted since a recent hike in taxes."

Impact:Considering Japan is among the world's largest economies, pros worry that an unexpected ripple could catch them off-guard, so they sell first and ask questions later.

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Worry #2—China: "No matter how low the estimates go for the purchasing managers' reports or import or export data or money supply data, the news still disappoints," Cramer said. "I think China's growth, at one time double digits, right now is falling from 7 percent to 5 percent. I know, I know, most countries would kill for that kind of growth, but for China that's not good."

Impact: Not only is China the world's second largest economy, but, as an emerging nation, there are real concerns on Wall Street that insufficient growth could trigger serious political upheaval. And that sends buyers to the sidelines, the "Mad Money" host says.

Worry #3—Ukraine: "I think this issue is at the fulcrum of much that goes wrong these days. Every time there is a provocation by Russia, we sell off; every time," said Cramer. "Some of that is our knee-jerk following of the selloff in Europe. Some of it is we worry about sanctions put on Russia that could end up slowing world growth."

Impact: If there was ever a wildcard in the market, it's Russian President Vladimir Putin. Cramer says he presents significant uncertainty to the market, which in turn prevents money from going into some higher risk assets.

Worry #4—U.S. bonds: "Bond prices are going higher and interest rates are going lower. Professionals fear this move because in a thriving economy, the opposite happens, money goes out of bonds and rates go higher."

Impact: Cramer says the Street fears the decline in interest rates more than anything, with pros wondering if rates signal something seriously wrong in the world. "As a result, nervous money managers dump stock furiously at a moment's notice," he said.

Although there are certainly other fears in the market, Cramer believes these motivate money flows on a daily basis.

That doesn't mean stocks can't rally, Cramer says, but if you own stocks make sure your seatbelts are fastened. Until the market comes to terms with its fears, or until the fears recede of their own accord, chances are, it's going to be a bumpy ride.